1. Field of the Invention
The present invention relates to a control arrangement for dental furnaces, especially microprocessor-controlled preheating furnaces or ovens with controlled heating and with limited rate in the rise of the heating temperature.
Dental furnaces of the above-mentioned type are generally employed as muffle or preheating furnaces for the purpose of preheating goods employed in the dental technology; for example, to preheat casting models which are embedded in the plaster or gypsum-like mass to a temperature which facilitates a problemless or satisfactory flow of the liquified material within even the narrowest passageways. The temperature which is necessary for this purpose is dependent upon the alloy which is employed and, for a casting of noble or precious metal, lies between about 700.degree. C. and 900.degree. C., and for usual precious metal replacement alloys and for model casting lies between about 1000.degree. C. and 1100.degree. C. Inasmuch as the embedding composition is subject to a certain expansion phenomenon, there is mostly required a dwelling period at an intermediate temperature of a magnitude of about 500.degree. C. This intermediate temperature is usually determined on the basis of the so-called Christobalite temperature.
2. Discussion of the Prior Art
In the year 1981, Kaltenbach & Voigt GmbH & Co., Federal Republic of Germany, brought a series of furnaces onto the market, thereby creating the first furnace which, besides the heretofore usual heating with pausing step, facilitated a controlled heating with a specified limited rate in the rise of the temperature. A rising temperature rate of 5.degree. C. per minute was considered to be optimum based on reasons of the material technology. Inasmuch as because of the new series of furnaces the preheating process was substantially improved and became more precisely regulatable, from then on there increased the demands for a preheating of certain embedding compositions which was equal to the system, and became always more complicated. The industry demanded a second and third pausing step, and even a heating sequence with a cooling phase.
Based on experience there was also ascertained that defective castings, which could be traced back to reasons relating to the process technology, could have two different causes; in essence:
1. Errors during preheating; for example, such as an inadequate maintaining of the pausing periods,
2. Error sources in the overall casting system; for example, excessively lengthy delay time between the removal from the furnace until casting or extensive heat reducing absorption by the steel of the casting apparatus.
For the formulation of a new furnace control there was consequently set the task of creating flexible program capabilities in order to be able to realize all currently required and, in the future contemplatable significant program sequences.
Inasmuch as this generates a large multiplicity of different programs, through the utilization of microprocessors the usually complicated input modes should be replaced by a simple and monitorably operable programming keyboard; in effect, the dental technician should be able to introduce new programs or program changes without practically any continual aid from the operating instructions. Predetermined programs which are always repeatedly used should hereby be able to be stored, so as to be called up or retrieved when needed.